Water the lavender consistently throughout its growing season. Keep the soil moist but not soggy with regular waterings. This encourages healthy plants that are better able to survive colder temperatures.
Delay pruning or cutting back your lavender until winter is over. Lavender grows like a shrub where new growth sprouts from existing stems. Cut it back only in the spring after new growth appears. Cut it back heavily in the spring to remove the woody, dead stems.
Avoid fertilizing lavender before winter unless the soil is extremely poor. Lavender generally does not need high levels of nutrients in its soil.
Cover small lavender plants and the area around them with a thick layer of mulch before the first frost. Mulch the soil and spread a plant blanket over taller plants. The mulch should be at least 2 or 3 inches thick. Remove the mulch and plant blanket in the spring after all danger of frost has passed.